1. Field of the Invention
The present invention relates to a flash discharge tube to be used, for example, to take a photograph, wherein the flash discharge tube comprises a trigger electrode composed of a transparent conductive film formed on a surface of a light-transmissive sealed tube made of a material such as glass. The present invention also relates to a method for producing the flash discharge tube.
2. Description of the Related Art
A flash discharge tube, which has been hitherto used, for example, to take a photograph, comprises a noble gas such as xenon enclosed in a columnar glass tube provided with a cathode electrode and an anode electrode disposed at both ends of the glass tube. The flash discharge tube further comprises a trigger electrode composed of a transparent conductive film containing a major component of tin oxide or the like formed on an outer circumferential surface of the glass tube.
In order to provide a means for improving the light emission efficiency of such a flash discharge tube, the present applicant has previously proposed a technique in which all or almost all of an area of the flash discharge tube for directly irradiating a photographic subject is formed with a portion in which no transparent conductive material is applied (see Japanese Laid-Open Utility Model Publication No. 60-141065). It has been demonstrated for the flash discharge tube concerning the proposed technique described above that the amount of light, which is obtained, for example, when only a back surface of the discharge tube is coated with the transparent conductive material, is increased by about 7% as compared with the amount of light which is obtained when the entire surface of the discharge tube is coated.
The flash discharge tube itself is extremely minute, and it is necessary to enclose the cathode and the anode in the glass tube together with the xenon gas. For this reason, in the conventional technique, when the flash discharge tube is produced, the entire production step is subdivided into a number of steps. Operations in the respective subdivided steps have been manually performed. Therefore, a problem arises in that the improvement in production efficiency of the flash discharge tube involves a limit as a matter of course.
The present invention has been made as a result of diligent investigations performed by the present applicant to follow the proposed technique, concerning the relationship between the light emission efficiency and the coating condition of the transparent conductive material. An object of the present invention is to provide a flash discharge tube and a method for producing the same excellent in light emission reliability so that a sufficient amount of light is obtained.
Another object of the present invention is to provide a method for producing the flash discharge tube, which makes it possible to realize fully automatic steps of producing the flash discharge tube, and achieve improvement in production efficiency of the flash discharge tube.
The above and other objects, features, and advantages of the present invention will become more apparent from the following description when taken in conjunction with the accompanying drawings in which a preferred embodiment of the present invention is shown by way of illustrative example.